Herein is described photosensitive members, imaging members, photoreceptors, or photoconductors useful in electrostatographic apparatuses, including printers, copiers, other reproductive devices, and digital apparatuses. In specific embodiments, described herein are photosensitive members having deletion control additives. In embodiments, the deletion control additives comprise a 3,4,9,10 perylenetetracarboxylic diimide compound. The deletion control additive provides, in embodiments, a better resistance to corona effluence and a more electrically sensitive device, hence increasing image quality.
Electrophotographic imaging members, including photoreceptors, photosensitive members, or photoconductors, typically include a photoconductive layer formed on an electrically conductive substrate or formed on layers between the substrate and photoconductive layer. The photoconductive layer is an insulator in the dark, so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated, and an image can be formed thereon, developed using a developer material, transferred to a copy substrate, and fused thereto to form a copy or print.
Many advanced imaging systems are based on the use of small diameter photoreceptor drums. The use of small diameter drums places a premium on photoreceptor life. A major factor limiting photoreceptor life in copiers and printers is wear. The use of small diameter drum photoreceptors exacerbates the wear problem because, for example, 3 to 10 revolutions are required to image a single letter size page. Multiple revolutions of a small diameter drum photoreceptor to reproduce a single letter size page can require up to 1 million cycles from the photoreceptor drum to obtain 100,000 prints, a desirable goal for commercial systems.
For low volume copiers and printers, bias charging rolls (BCR) are desirable because little or no ozone is produced during image cycling. However, the microcorona generated by the BCR during charging, damages the photoreceptor, resulting in rapid wear of the imaging surface, for example, the exposed surface of the charge transport layer. More specifically, wear rates can be as high as about 16 microns per 100,000 imaging cycles. Similar problems are encountered with bias transfer roll (BTR) systems.
One approach to achieving longer photoreceptor drum life is to form a protective overcoat on the imaging surface, for example, the charge transporting layer of a photoreceptor. This overcoat layer must satisfy many requirements, including transporting holes, resisting image deletion, resisting wear, and avoidance of perturbation of underlying layers during coating.
Various overcoats employing alcohol soluble polyamides have been proposed in the prior art. One of the earliest ones is an overcoat comprising an alcohol soluble polyamide without any methyl methoxy groups (Elvamide 80630®) containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine. This overcoat is described in U.S. Pat. No. 5,368,967, the entire disclosure thereof being incorporated herein by reference. Although this overcoat had very low wear rates in machines employing corotrons for charging, the wear rates were higher in machines employing BCR.
A crosslinked polyamide overcoat overcame this shortcoming. This overcoat comprised a crosslinked polyamide, referred to as Luckamide®, containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine. In order to achieve crosslinking, a polyamide polymer having N-methoxymethyl groups (Luckamide®) was employed along with a catalyst such as oxalic acid. This tough overcoat is described in U.S. Pat. No. 5,702,854, the entire disclosure thereof being incorporated herein by reference. With this overcoat, very low wear rates were obtained in machines employing bias charging rolls (BCR) and bias transfer rolls (BTR). Durable photoreceptor overcoatings containing crosslinked polyamide (i.e., Luckamide®) containing N,N′-diphenyl-N,N′-bis(3-hydroxyphenyl)-(1,1′-biphenyl)-4,4′-diamine (DHTPD) (Luckamide®-DHTPD) have been prepared using oxalic acid and trioxane to improve photoreceptor life by at least a factor of 3 to 4. Such improvement in the bias charging roll wear resistance involved crosslinking of Luckamide® under heat treatment, for example, 110° C.–120° C. for 30 minutes.
However, adhesion of this overcoat to certain photoreceptor charge transport layers, containing certain polycarbonates (e.g., Z-type 300) and charge transport materials such as bis-N,N-(3,4-dimethylphenyl)-N-(4-biphenyl)amine and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine, is greatly reduced under some drying conditions. Polyvinyl butyral (PVB) was added to the formulation to promote the poor adhesion between the overcoat layer and the charge transport layer. The addition of PVB to the Luckamide overcoat formulation is described in U.S. Pat. No. 6,207,334, the entire disclosure thereof being incorporated herein by reference.
One of the most noticeable problems in current organic photoreceptors is lateral charge migration (LCM), which results in the deletion of electrophotographic images. The primary cause of LCM is the increased conductivity of the photoreceptor surface, which results in charge movement of the latent electrostatic image. The development of charge pattern results in toned images that are less precise than the originals. The increase in surface conductivity is believed to be primarily due to oxidation of the charge transport molecule by nitrous oxides effluents from bias charging roll and corona charging devices. The problem is particularly evident in some machines, wherein there are several charging corotrons, and in photoreceptors where there is little surface wear on the photoreceptor and the conductive oxidized species are not worn away. The latter is the case with crosslinked polyamide overcoats.
To eliminate LCM, tetrakis methylene(3,5-di-tert-butyl-4-hydroxy hydrocinnamate)methane(Irganox 1010), butylated hydroxytoluene (BHT), bis(4-diethylamino-2-methylphenyl)phenylmethane(BDETPM), bis-[2-methyl-4-(N-2-hydroxyethyl-N-ethyl-aminophenyl)]-phenylmethane (DHTPM), and the like, have been added to the charge transport layer of organic photoreceptors with arylamine charge transporting species. To eliminate gross macroscopic deletions of Kanji characters in the A zone, BDETPM or DHTPM has been added to the polyamide overcoat formulations. However, in the case of the polyamide overcoat, all these known deletion control additives have been shown to be inadequate.
It appears that deletion is most apparent in the polyamide overcoat because of its extreme resistance to wear (10 nm/kilocycle with bias charging rolls and 4 nm/kilocycle with scorotron charging). Because the oxidized surface does not wear off appreciably, deletion from the polyamide overcoat is more apparent than in polycarbonate charge transport layers where the greater wear rates continually refresh the photoconductor surface. Therefore, new and improved deletion control additives are needed to preserve image quality in polyamide overcoated photoreceptor drums and belts, by reducing or eliminating lateral charge migration and the resultant print defects caused by corona effluents on photoreceptor surfaces. It is further desired to provide an overcoat for photoreceptors that accelerates hole transport through the overcoat layer to eliminate or reduce lateral charge migration. In addition, it is also desired to provide a photoreceptor coating that allows the preservation of half-toned and high frequency print features of 300 dots per inch and less to be maintained for more than 2,000 continuous prints (or at least 8,000 photoreceptor cycles) in the A, B and C zones.